The present invention relates to a device and a method for detecting an approach or a touch related to at least one sensor element, in particular for operating an electrical appliance. Further, the present invention relates to a series arrangement of at least two such devices.
Detecting or determining an approach or a touch related to at least one sensor element is of great significance for operating, monitoring and/or controlling an electrical appliance. Among the devices of interest are such devices that allow to determine a position related to areas of a closed surface that are designed to look like keys. In the past, the individual operating elements of an operating panel have been embodied as discrete mechanical or electro-mechanical keys or switches. In order to operate a key, the cover of the operating panel required openings, through which dirt and fluids could enter into the operating panel. One idea was to cover the keys with a layer of rubber, but such layer did not have a sufficient durability and the feel of the surface was not satisfactory.
In order to detect an approach of an object towards a closed surface or a touch of an object on a closed surface, methods based on an electrical principle have been applied. The reasoning is, that a corresponding object, in particular a finger of a human hand, introduces resistive and/or capacitive changes that can be detected and based on which the position of an object can be determined. Quite often the technical concept of a capacitive touch switch has been employed.
The principle of a capacitive touch switch has been known for a long time. For example, in the context of providing operating areas for ceramic stove tops, DE 80 33 570 U1 discloses to provide a large capacitive area at the top surface and two smaller capacitive areas at the back of the ceramic plate. An alternating current is applied to one of the smaller capacitive plates. In the other smaller capacitive plate, another alternating current is detected. If the operating area is touched by a finger, the capacitive arrangement goes off-tune, which can be detected via corresponding electronics and which can be understood as “pressing” the capacitive touch switch.
Document EP 1 416 636 A2 shows another arrangement for a capacitive touch switch, where a body of foamed material comprises electrically conductive areas having a sensor element top surface and isolating areas, which are arranged along the extent of a ceramic plate in an alternating manner. Thereby, a type of “string material” can be produced where capacitive touch switches can be produced that are arranged side by side.
EP 0 859 467 B1 discloses to provide a capacitive touch switch with a sensor key, which acts as one pole of a capacitor, wherein the sensor key is made of a flexible, regionally extending, and electrically conducting material, which is variable in its shape and which is arranged on a printed circuit board and acts as a bridge for the distance between a cover plate and the printed circuit board, wherein a certain compression stress is maintained.
DE 10 2004 038 872 A1 discloses a touch switch for an operating panel of an electric device such as a stove top. The switch comprises a sensor element with two sensor areas, which again comprise one or more triangle-shaped sub-areas. Control signals are applied to the sensor areas and are partially uncoupled, when a touch with a finger occurs, corresponding to the amount of the area covered by the finger. The remaining signal is fed into a microcontroller for comparison, in order to detect the position of the touch as a function of the ratio of the remaining signal strengths and the areas covered.
Against this background, an object of the present invention is to provide an improved device for detecting an approach or a touch related to at least one sensor element, in particular for operating an electric appliance, the device allowing for cost-saving and efficient production in large quantities. It is desired that the use of a plurality of devices, in particular in a series arrangement, can be easily realized. It is a further object to provide a corresponding improved method for detecting an approach or a touch related to at least one sensor element and a corresponding series arrangement.